The present invention is directed toward rubber compositions and vulcanizates that exhibit damping over a wide temperature and frequency range. More particularly, these compositions and vulcanizates include a damping component, which includes a comb polymer. In a preferred embodiment the vulcanizates are tire components.
Damping is the absorption of energy, such as vibrational or sound energy, by a material in contact with the source of that energy. Damping vibrational energy from a number of sources such as motors and engines can be desirable.
Viscoelastic materials are often employed for damping applications. Energy is absorbed by the viscoelastic material and converted into heat. Ideally, viscoelastic materials employed for damping are effective over a wide range of temperatures and frequencies.
The viscoelastic nature of materials can be mathematically represented by the formula G*=Gxe2x80x2+iGxe2x80x3 where G* is the complex shear modulus, Gxe2x80x2 is the elastic or storage modulus, Gxe2x80x3 is the viscous or loss modulus, and i={square root over (xe2x88x921)}. The damping effectiveness of viscoelastic materials can be quantified by measuring viscoelastic response to a periodic stress or strain. Results of dynamic mechanical tests are generally given in terms of Gxe2x80x2 and Gxe2x80x3, where Gxe2x80x3 is directly related to the amount of mechanical energy converted to heat, i.e., damping.
The ratio of Gxe2x80x3 to Gxe2x80x2 is often referred to as tan xcex4,       tan    ⁢          xe2x80x83        ⁢    δ    =            G      xe2x80x3              G      xe2x80x2      
which quantifies a material""s ability to dissipate mechanical energy versus the purely elastic storage of mechanical motion during one cycle of oscillatory movement. Tan xcex4 can be measured by a dynamic analyzer, which can sweep many frequencies at a fixed temperature, then repeat that sweep at several other temperatures, followed by the development of a master curve of tan xcex4 versus frequency by curve alignment. An alternate method measures tan xcex4 at constant frequency over a temperature range.
In common practice, the tan xcex4 of a material is usually broadened by taking advantage of the glass transition temperature of several materials within a temperature range. U.S. Pat. No. 5,494,981 teaches a composition that comprises resins that are cured in sequential fashion by using a single catalyst. The catalyst is a Bronsted acid that activates an epoxy resin component and then activates cyanate trimerization into polytriazines. The composition provides a glass transition damping peak around 100xc2x0 C. and is understood to be heat stable over a temperature range of about 0xc2x0 to at least 300xc2x0 C.
Although numerous compositions are known for damping, there is a need for improved damping compositions that exhibit a high degree of damping over a wide range of temperatures and frequencies without involving glass transition peaks. Enhancing hysteresis (tan xcex4) by using superposition of glass transition peaks is not desirable because the modulus of the material drops dramatically at or about the glass transition temperature.